1. Field of the Invention
The present invention is directed to an anchor for use in a friable material, particularly to a self-drilling anchor to be used in drywall mounted to a member.
2. Description of the Related Art
Because drywall is a friable material, mounting articles thereto can be difficult. In the past, at least three methods have been used. For light weight articles, small plastic expansion anchors have been used. These expansion anchors have typically required three steps to install: first, a hole is drilled into the drywall; second, the anchor insert is driven into the drilled hole; and finally, a threaded fastener is advanced into the anchor, spreading the anchor into engagement with the drywall. However, expansion anchors can typically hold light loads only.
For heavy duty applications, toggle bolts have been used. While toggle bolts have been effective, they are also generally expensive because they involve parts which must move relative to one another. Toggle bolts also have been known to be difficult to install.
Self-drilling anchors for mounting heavier loads also have been used. These self-drilling anchors typically are installed by drilling into the drywall with the anchor itself. The anchor also includes threading having a high thread height to provide a high pullout in the drywall. Examples of self-drilling anchors include the anchor sold under the trademark E-Z ANCOR manufactured by ITW Buildex, and those disclosed in U.S. Pat. Nos. 4,601,625, 5,190,425, and 5,558,479, all of which are assigned to the assignee of this application.
Self-drilling anchors have proved effective for holding higher loads when installed in drywall alone. However, in most cases the drywall is mounted to wood support members, or studs, that are unseen by the user, and typically the location of these support members are unknown and unchecked by the user. When a user of a typical self-drilling fastener attempts to install the anchor in drywall at a location of a support member, the anchor is unable to drill into the support member, causing the anchor to spin in place so that the anchor's high threading strips out the drywall, resulting in failure of the anchor and creating an unsightly scar on the wall. Even if the anchor is able to drill into the support member slightly, the anchors have been known to tightly engage the support member and break due to torsion on the anchor.
What is needed is a self-drilling fastener for use in drywall that can be installed either in drywall only, or in drywall and a support member capable of handling a heavy load.